Hand-held microwave intra-oral dental system

ABSTRACT

A hand-held microwave system for intra-oral dentistry utilizes microwave energy to cure polymer materials intra-orally so as to produce dental composites having improved physical characteristics, and also utilizes microwave energy to detect the presence of and to preferentially heat caries or cavities, thereby disinfecting and therapeutically treating the caries in a potentially non-invasive manner. The intra-oral polymerization process can be accomplished with less overall energy and with composite-matrices that maximally absorb the microwave energy so as to reduce heating of adjacent tissue. The antenna of a hand-held version of the intra-oral microwave system is also advantageously designed to detect the presence of and to preferentially heat caries or cavities, thereby disinfecting and therapeutically treating the caries in a potentially non-invasive manner. A method and product by process for the system are also disclosed.

FIELD OF THE INVENTION

The present invention relates generally to the field of dentistry. Morespecifically, the present invention relates to a hand-held microwavesystem for intra-oral dentistry that utilizes microwave energy to curepolymer materials intra-orally so as to produce dental composites havingimproved physical characteristics, and also utilizes microwave energy todetect the presence of and to preferentially heat caries or cavities,thereby disinfecting and therapeutically treating the caries in apotentially non-invasive manner.

BACKGROUND OF THE INVENTION

The use of polymer materials in the dental arts for the restoration oflost or damaged teeth is well known. Such uses fall into two generalcategories: (i) the use of polymer materials to produce dentalprosthetics, such as dentures, bridges and crowns, that are eitherpermanent or removable articles, and (ii) the use of polymer materialsto create dental composites for fillings to repair teeth instead ofusing conventional amalgam fillings or as veneers to refinish toothenamel surfaces. The first category of dental articles, dentalprosthetics, are created outside of the patient (i.e., extra-oral),typically by making an impression of what the desired article shouldlook like and then molding the article to match the impression. Thesecond category of dental articles, dental composites, are createddirectly in the patient's mouth (i.e., intra-oral) as fillings orveneers to repair or resurface teeth.

The use of microwave energy in the form of a commercial microwave ovenused to process dental prosthetics extra-orally is well known. Varioustypes of flasks and molding equipment that can be used in conjunctionwith a commercial microwave oven for processing and curing dentalarticles made of polymers have been developed as described, for example,in U.S. Pat. Nos. 4,971,735, 5,151,279, 5,324,186 and 5,510,411,European Patent No. 0 687 451 A2 and Japanese Patent No. JP7031632A.Examples of polymer resin matrices that are specifically formulated toutilize microwave energy supplied by a commercial microwave oven for thethermal polymerization of the polymers into dental articles are shown inU.S. Pat. Nos. 4,873,269, and 5,218,070 and Canadian Patent No.2,148,436. The impact of the role played by the polymer initiator in amicrowave cured resin matrix has been evaluated by Urabe H. et al. in“Influence of polymerization initiator for base monomer on microwavecuring of composite resin inlays,” Journal of Oral Rehabilitation, Vol.26, pp. 442-46 (1999). The repair of dentures and related articles usingmicrowave processing is also described in Turck MD et al, “Microwaveprocessing for dentures, relines, repairs and rebases,” The Journal ofProsthetic Dentistry, Vol. 69, No. 3, pp. 340-43 (1993). Generally,dentures cured by commercial microwave ovens have improved mechanicalproperties, and often have better adaptation than those cured byconventional water-bath method. The primary advantage of microwavecuring, however, is the reduced processing times which can be shortenedfrom 8 hours or more to as little as a few minutes.

There had been relatively little research, however, into the potentialimpact of the microwave energy itself on the polymerization process fordental prosthetics. The research that has been done has generallyfocused on the duty cycle used for the microwave oven curing process.The impact on porosity of denture material cured using lower wattage,longer duration microwave cure times (i.e., a lower duty cycle for alonger time) versus higher wattage, shorter duration microwave curetimes (i.e., a higher duty cycle for a shorter time) is compared inAlkhatib MB, et al. “Comparison of microwave-polymerized denture baseresins,” The International Journal of Prothodontics, Vol. 3, No. 2, pp.249-55 (1990). European Patent No. 0 193 514 BI describes a microwaveprocessing system for dental prosthetics that has a magnetron, awaveguide, a surface radiating antenna, a flask, and a temperaturesensor that is inserted in the flask and connected to a regulatingprocessor. The regulating processor limits the temperature in the flaskas measured by the temperature sensor by turning on and off themagnetron based on frequency modulation of the duty cycle. Although notused for polymerization of dental articles, U.S. Pat. No. 5,645,748 doesdescribe a microwave system for sterilization that controls duty cycleof a microwave oven for the purpose of minimize arcing caused bymetallic surgical or dental instruments.

With respect to the second category of dental articles created usingpolymer materials, dental composites formed of polymer matrix-compositesare increasingly being used as an alternative to mercury-containingdental amalgam for aesthetic and restorative dental materials. Thesekinds of polymer matrix-composites are usually photo polymerizable inthat they are cured using some kind of light instead of heat. Generally,the polymer matrix-composite is based on a photo polymerizablepolyfunctional methacrylate compound that can be used alone or asmixture with monomethacrylates, light sensitive cure initiators pigmentsand fillers in a mixture with various comonomers such astriethyleneglycol dimethacrylate. Although the half-life of thesepolymer matrix-composites cured by light is on the order of 5-8 yearsand therefore they tend to wear out earlier than conventional dentalamalgams, the enhanced biofunctionalilty and more pleasing aestheticqualities of these polymer matrix-composites have gained favor overconventional dental amalgams.

The main deficiencies of polymer composite resins used as dentalcomposites are surface degradation which leads to inadequate wearresistance, polymerization shrinkage and a lack of density. In additionto the problems previously described for dental prosthetics,micro-shrinkage of polymer dental composites produces interfacial gapson the surface of the composites, which can results in microleakagethrough the dental composite. The long-term consequence of suchmicroleakage can be bacterial penetration into the tooth that can causea variety of adverse reactions in the tooth such as pulp damage, toothsensitivity, possible pulpal death and loss of adhesion of the dentalcomposite.

Improving the degree of polymerization of polymer matrix-composites isgenerally considered to be one way of improving their physical andbiofunctionality characteristics of polymer dental composites as thiswould lead to stronger dental composites that are less susceptible todegradation, wear and fracture. It would also lead to improvedbiocompatibility, since there would be reduced amounts of uncuredmonomer that could act as a biohazard.

Unlike polymer dental prosthetics, however, the curing of polymermatrix-composites by application of thermal energy generally has notbeen used to date. Obviously, in the case of the conventional thermalwater-bath process, it would be impractical to require a patient toremain at the dentist's office for up to 8 hours with their mouth openand with a tooth immersed in a hot water bath in order to set athermally polymerizable matrix-composite. It is also not possible toplace a patient's mouth into a commercial microwave oven to set athermally polymerizable matrix-composite.

While there are numerous hand-held medical catheter devices that utilizeradio frequency and microwave energy to perform ablations and similarheating operations, for example, in the vascular system of a patient,there have been relatively few uses of thermal or electrical energyapplied to hand-held dental tools for intra-oral applications. Therehave been a few hand-held dental probes that utilize an electricallyresistive heated tip for diagnosis of dental decay or for melting asealing material in an intra-oral context as described, for example, inU.S. Pat. Nos. 4,527,560 and 5,893,713. U.S. Pat. No. 5,421,727describes the use of radio frequency/microwave energy as part of ahand-held endodontic root canal device to raise the temperature of theinterior of the tooth adjacent to the root canel, thereby tending todisinfect the tooth during the root canal procedure as a result of theincreased temperature.

The extra-oral use of microwave energy for the purpose of characterizingdental decay in extracted teeth has been described by N. Hoshi et al in“Application of Microwaves and Millimeter Waves for the Characterizationof Teeth for Dental Diagnosis and Treatment,” IEEE Transactions onMicrowave Theory and Techniques, June 1998, Vol. 46, No. 6, pp. 834-38.This study confirmed the higher absorbancy behavior of carious lesionsin extracted teeth when irradiated by microwave energy as compared tothe lower absorbancy of such microwave energy by healthy enamel anddentin.

While existing photo polymerizable dental composites have enjoyedsuccess as compared to conventional dental amalgams for dental fillingsand veneers, it would be desirable to further improve the uniformity anddegree of conversion of monomers into polymer chains in thepolymerization process in order to produce even better dentalcomposites. It would also be desirable to provide a dental tool thatcould take advantage of the use of microwave energy for purposes otherthan the polymerization of dental composites.

SUMMARY OF THE INVENTION

The present invention is a hand-held microwave system for intra-oraldentistry that utilizes microwave energy to cure polymer materialsintra-orally so as to produce dental composites having improved physicalcharacteristics, and also utilizes microwave energy to detect thepresence of and to preferentially heat caries or cavities, therebydisinfecting and therapeutically treating the caries in a potentiallynon-invasive manner. The intra-oral polymerization process can beaccomplished with less overall energy and with composite-matrices thatmaximally absorb the microwave energy so as to reduce heating ofadjacent tissue. The antenna of a hand-held version of the intra-oralmicrowave system is also advantageously designed to detect the presenceof and to preferentially heat caries or cavities, thereby disinfectingand therapeutically treating the caries in a potentially non-invasivemanner.

The hand-held dental tool is designed to apply continuous microwaveenergy in accordance for use in creating dental composites directly in apatient's mouth. Microwave energy having a frequency of between 1 GHz to50 GHz, and preferably between 14 GHz to 24 GHz, is applied by anantenna at the distal end of the hand-held tool which is connected via aconductor or wave guide to a microwave generator that supplies low powermicrowave energy in response to precisely controlled voltages.Preferably, the microwave energy power is less than about 10 W andideally between 3 W and 5 W and the control voltages operate between 12V and 65 V, depending upon the desired curing time and the particularcomposition of the resin matrix to be cured. Preferably, the antenna anddistal end of the hand-held tool are structured to enable the operatorto exert some degree of pressure on the composite resin-matrix in themouth while it is being cured by the application of microwave energy.The low power microwave energy provided by the hand-held tool of thisembodiment is safe for intermittent human exposure as the power andfrequency ranges emitted by the antenna are similar to that emitted bycellular telephones.

One of the advantages of the hand-held dental tool is that it can alsoserve as a tool for non-invasively detecting and/or treating caries orcavities. Carious tooth tissue consists of demineralized and softenedand moist tooth enamel or dentin, and contains micro-organisms. If thecarious tooth tissue has not degraded to the point where the physicalproperties of the tooth are compromised, it is possible for the carioustooth tissue to recalcify and reharden if the micro-organisms causingthe carious tooth tissue can be killed and the tooth can be kept underaseptic conditions. Infected tooth tissue which is not removed or notkept under aseptic conditions will remain as an active carious lesion,and will continue to cause progressive and destructive loss of toothtissue. The use of the continuous microwave energy supplied by thehand-held dental tool embodiment of the present invention can eliminateor reduce the infection caused by the micro-organisms as the type ofmicrowave energy is selected to preferentially heat and destroy themicro-organisms in the carious tooth tissue. In some cases, thehand-held dental tool can be used to kill the micro-organisms internalto the tooth tissue by the use of microwave energy and then a sealantcan be applied to the exterior of the tooth which will be sufficient tokeep an aseptic environment and promote the recalcification of theunderlying tooth tissue. In other cases, portions of the carious toothtissue may need to be removed and the hand-held tool can be used to killthe micro-organisms both internal to the tooth tissue and on the surfaceof the cavity. Once the micro-organisms have been destroyed, a polymerdental composite can be applied to the cavity. The polymer dentalcomposite is preferably microwave cured using the hand-held dental toolto seal the treated tooth tissue and provide additional physical andstructural support for the cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional side view showing the details of apreferred embodiment of the polymer material injector system.

FIG. 2 is an isometric view of a hand-held dental tool embodiment of thepresent invention.

FIGS. 3-6 are various embodiments of antennas for the distal end of thehand-held dental tool embodiment of FIG. 2.

FIG. 7 is an electrical schematic of the control circuitry forgenerating the microwave energy in the hand-held dental tool embodimentshown in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the various figures, a detailed description of thepreferred embodiment of the present invention will be presented. Variouscomplex dielectric permittivity, temperature and distribution patternstudies of microwave heated teeth and simulations of specific absorptionrate distribution have been conducted as part of the research into thepresent invention. The complex permittivity was measured on differenttypes of dental tissues, using extracted teeth, including enamel, dentinand caries. Reflective coefficients have been obtained using a networkanalyzer. The characteristics of enamel caries and dentin are different.The dielectric loss factor of caries is fairly higher than that ofnormal healthy parts particularly in the millimetric wave in thefrequency between 12 GHz to 25 GHz. When the tooth is exposed tomillimetric microwaves in this range, caries are preferentially heated.Temperature rise can kill the microorganisms in caries. Control and orextinction of microorganism slows or stops the progress of caries,permitting previously carious tissue to recalcify by biological latentsupport of the pulp. Temperature distribution measurement withmicrowaves heating reveals that the temperature of caries is higher thanthat of normal tooth tissue. These properties are used with theprovisions of this invention for the diagnostic and treatment of teethhaving caries and subsequent internal heat conditioning and or curing ofprovided dental restorative materials. When dielectric loss factor ishigher, the absorption of microwave is better and local temperature ishigher. Microwave energy heats by radiation and is able to penetratethrough various substances including desiccated tissue and thus cancreate an addressed effect.

To understand the details on which the preferred embodiment is based, itis helpful to understand how microwave energy is generated and absorbed.The microwave energy absorbed by a given dental materials is governed bythe following equation:

P=2πfE ²ε′ tan δ

where:

P=Power density (w/m³)

f=frequency

E=electrical field strength (rms)

ε′=dielectric constant of the dental material

tan δ=dielectric loss factor.

This equation shows that in order to determine the microwave energy interms of the incident microwave power level absorbed by a dentalarticle, both the applied electric field strength and the dielectricmaterial characteristics must be known. One of the difficulties inproperly evaluating this equation is that when a curable dielectricresinous material is polymerized, its microwave absorption isdrastically reduced because the dielectric constant of the materialchanges as a result of the polymerization process. Similarly, whenmicrowave energy is directed to a tooth containing a carious lesion, theabsorption of the microwave energy changes. The present inventionutilizes this difference in absorption as a mechanism for identifyingcarious lesions with the same hand-held dental tool that can be used tonon-invasively treat those caries,

In one embodiment as shown in FIG. 7, a system of caries control in anon invasive atraumatic way, without surgical burs entry and with areduced risk and necessity of exposing the dental pulp organ comprise, ahand held microwave applicator with a sufficient microwave powerdelivery capability is provided to heat the dental tissues orrestorative materials. The electronic circuit diagram of FIG. 7 isdesigned to suit small microwave generators such as an oscillationsource coupled with a RF power amplifier or impatt diodes or similarsolid state or transistorized microwave emitters with an output power ofabout 2 to 5 watts which requires usually an electrical voltage of about60 DC. The bias voltage is applied through a high impedance line (56) inorder to limit the perturbation of electromagnetic signals. A powersupply module is provided with a current and voltage limiting mean topermit the polarization of the impatt diode in the specific limits witha resonant circuit (57), such as a 50 ohms line, having a lengthpreferably equal to the half of the length of the selected frequency.The length of the line may be calculated with the following equation:L=3×10⁸/2fε_(cff) ^(½). One end of the “resonator” is connected to theimpatt diode (58) and the other end of it is coupled (59) to atransmission line including an isolator (60) to provide isolation of themicrowave source from the rest of the circuit in order to avoidfrequency variations, caused by a mismatch of the output (61). A coupler(62) having a coupling of about −15 dB permit a sampling of the signalemitted by the microwave generator in order to measure the incident andreflected power levels. The couplers should be perfectly matched at bothextremities to permit precise measurements. Matching circuit (63) at theinput and the output as well as load resistors permit achievement of anadaptation at each ends, equal or better than −15 dB. Detecting diodes(64) rectify the radio frequencies signal in order to convert the powerto a dc voltage which can advantageously be subsequently transmitted toa micro controller or a “ADC” analog digital converter which convertsthis voltage to a digital signal for an appropriate processing of theacquired information and the precise monitoring and the control of themicrowaves energy delivered to the dental target. The controller is ameans of setting the power level, exposure cycles, processing modes, andmay also be used in the selection of the frequency of microwavegeneration. As shown in FIG. 2, the control of the microwave source ispreferably made by a selector (65), located on the device, allowing theoperator to set different power levels and modes. Between the tipantenna and the microwave source or amplifier, a shielded cable (66) orwave guide, as short as possible is used to operatively transmit themicrowave power to the head antenna.

A suitable connector preferably permits the interchange of differentprovided head antennas to match different applications and enhanceenergy transmission and deposition on the dental target. A means ofelectrical supply (67), such as a shielded cable, connects the mobileapplicator to the power supply. The hand held applicator may be equippedwith a water cooling system (68) and a digital display (69).

One head antenna (70) as shown in FIG. 4 is provided for therapeuticpurposes to target teeth and treat, heat or detect dental caries, and ismade of a highly conductive metal such as copper, platinum or gold,plated or not, having the format of a rectangular or a loop shaped bandof which one end is connected to the inner and the outer conductors ofthe transmission line.

One provided monopole head antenna has the form of an I as shown in FIG.5. This applicator is made for example by stripping the outer jacket andthe outer conductor of a coaxial shielded cable, the inner conductor anddielectric (Teflon) constitute the applicator. To increase thedirectivity of the radiating microwave energy, a loaded I-applicator(71) having an increased forwarding effect may be made by placing aplatinum ring over the outer conductor of the coaxial cable andsoldering a platinum rod on the inner conductor of the antenna.

Another provided head antenna (72) as shown in FIG. 6 is made of amicrostrip which may be made of miscible polymeric or other conductivematerials, having the format for example of a square metal skin ispositioned on a dielectric substrate with a ground plane on its back.

An electrically shielded temperature probe may be embedded in the headof the hand held applicator antenna to provide a means of monitoring thetemperature of the heated target for judging the efficiency of tissueheating and to avoid sudden temperature rises.

The provided head antenna designs help in achieving good impedancematching and effective delivery of microwave for internal heatconditioning of dental targets. As shown in FIG. 3, a means of safelycontaining any leakage of microwave energy close to the irradiationspace can be used such as the disclosed head antenna choke (73), made ofmicrowave absorbing materials.

Preferably, the antennas are made with a portion that is strong andflexible enough to be used as a positioning and compression tool for thepasty resin matrix for the dental composite. The loop and patch antennamay preferably carry negative dental molds to aid in the formation ofthe dental composite. Alternatively, a minaturized version of a manualresin injector, such as previously described in connection with FIG. 1,may be provided to deliver the pasty resin matrix for the dentalcomposite as part of the hand-held tool. While the hand-held tool ispreferably used in an intra-oral application with dental composites, itwill be recognized that the hand-held tool can also be used in thedental office, for example, to accomplish repairs or welds of dentalprosthetics devices as well.

In one embodiment as shown in FIG. 1, an economic manual fluid resinpressurization and injection device (46) is provided to remove the needof being connected to an external pressurized fluid source. A mechanicalforce accumulator such as a spring (47) is compressed by turning theinternally threaded cylinder (48) while holding the device handle (49).A force boosting piston (50) is especially useful for molding andfilling of composite curable dental materials. The injection nozzle andthe piston acts as previously described. When under a hydraulicpressure, the piston (39) forces the material from its compartmentthrough the injector (40). The piston (39) is advantageously equippedwith sealing joints (44). This embodiment can be minaturized andemployed with the hand-held intra-oral microwave applicator.

In general, various polymer based material compositions are useful forthe construction of dental devices. These compositions may be used inthe filling of teeth and the construction of appliances used forreplacing teeth and other oral structures.

One preferred composition for dental composites suited to be formed andhardened in accordance with the providing of this invention consists ofa polymerizable mixture including one or a selection from the largefamily of polyfunctional methacrylate esters, and oligomers includingthe compound prepared from one molecule of bisphenol A and two moleculesof glycidyl methacrylate called 2,2bis[4(2-hydroxy-3methacryloyloxy-propyloxy)-phenyl] propane, known as Bis-GMA for itslower degree of shrinkage and/or 2,2-bis[4-methacryloxyethoxy)Phenyl]propane for its good water resistance properties. Other monomers, suchas triethyleneglycol dimethacrylate for viscosity reduction, urethanedimethacrylates, spiro orthocarbontes, etc are advantageously employedin admixture with silanized inorganic fillers and organic fillers,coupling agents, microwave sensitive cure initiation system includingorganic peroxides and amines and color pigments are advantageouslyadded. The weight of the fillers as an overall weight of the compositeis preferably in the range of 30 to 90% and include silanized silicondioxide particles.

In one embodiment, compositions specially suitable for making dentalremovable appliances such as dentures is provided which comprise aliquid and a powdery component. The liquid component in accordance withthe invention contains preferably from 40% to 90% of mono-, di-, tri, ormultifunctional acrylic monomer, a cross-linking agent, a plasticizer, astabilizer. an accelerator and color pigments. The mono-, di, tri, ormultifinctional acrylic monomer in accordance with the invention arewithin the scope of the formula:

where R1 in accordance with the invention is hydrogen, alkyl,substituted alkyl group, cyclic hydrocarbon, benzyl, ether, hydroxyalkyland R2 is hydrogen, halogen, alkyl, substituted alkyl or cyclichydrocarbon group.

Monomers within the scope of the following formula are also particularlysuitable to the invention:

wherein R is an acrylic-free organic moiety, R₁ is hydrogen, hologen,halogen, alkyl, substituted alkyl or cyano radical and n is an integerfrom 1 to 20 and m is an integer from 1 to 1000. These monomers may beused alone or in admixture.

The microwave sensitive initiators in accordance with the inventionincludes benzoyl and peroxide, dilauroyl peroxide up to 2,5%. Thepolymerization accelerator in accordance with the invention is aquaternary ammonium chloride, which is easily soluble in themethacrylate monomers and reacts with barbituric acid derivatives. Apreferred compounds are the quatemary ammonium with an alkyl of 1 to 20carbons, such as, dodecyltrimethylammonium. These quaternary ammoniumchlorides may be added in alone or in admixture from 0,09 to 1,5%. Thecrosslinking agent in accordance with the provided microwave hardeningmaterial compositions is a polyfunctional monomer wherein at least twocarbon-carbon double bonds, such as 1,3-butanediol dimethacrylate,1,4-butanediol dimethacrylate, 1,4-butanediol divinyl ether, di(ethyleneglycol) dimethacrylate, di(ethylene glycol) divinyl ether,pentaerythritol diacrylate monostearate, ethylene glycol dimethacrylate,trimetylolpropane trimethacrylate, pentaerythritol triacrylate,pentaerythritol tetraacrylate, trimetylolpropane triacrylate. Thecrosslinking agents may be used alone or in admixture.

Polymerization promoters for the monomers of the provided curablematerial compositions for the present invention are useful because theyrapidly react with the quaternary ammonium chloride to produce radicals,which promotes a rapid and uniform polymerization in the composition anda higher degree of conversion. The barbituric acid derivative inaccordance with the invention include 1,3,5-trimethylbarbituric acid,1,3-dimethyl-5-isobutylbarbituric acid, 1,3-dimethyl-5-phenylbarbituricacid, 5-n-butylbarbituric acid, 5-ethylbarbituric acid,1-cyclohexyl-5-ethylbarbituric acid and 1-benzyl-5-phenylbarbituricacid. These acid derivatives may be used alone or in admixture in verysmall amounts. The polymerization stabilizers comprise hydroquinone,hydroquinone monomethyl ether or 4-ethoxyphenol which are usually addedto the liquid component of dental compositions (up to 4%). Theplasticizer in accordance with the invention is generally a lowmolecular weight ester, such as dibutyl phthalate or phosphates .

The composition for a one component microwavable curable material systemin accordance with this invention is approximately the same as the onefor the two component materials with some variations mainly in theinitiation system. Preferred initiators for a one component dentalcomposition for denture or such need to be thermally stable at room orhigher temperatures such as 50° C. and initiate polymerization at highertemperatures such as benzopinacole, tert-butyleperbenzoate, and2,2′dichlorobenzopinacol.

The powder component in accordance with the invention includes from 20%to 80% of mono-di-tri, or multifunctional acrylic or acrylate esterpolymer. The powder may advantageously include from 5% to 40% of acopolymer. The powder component in accordance with the invention mayadvantageously include from 0,1% to 3% of an initiator for radicalpolymerization including organic peroxides such as benzoyl peroxide anddilauroyl peroxide. The powder component in accordance with theinvention can include up to 1% of a barbituric acid derivative topromote chemical reaction. The mono-, di, tri, or multifunctionalacrylic polymer used in denture base in accordance with the inventionare:

where the R1 in accordance with the invention is hydrogen, alkyl,substituted alkyl group, cyclic hydrocarbon, benzyl, ether,hydroxyalkyl, R2 is hydrogen, halogen, alkyl, substituted alkyl groupand n is an integer at least equal to 2. The copolymer in accordancewith this invention are mainly composed of methyl methacrylate polymeror a mixture of methyl methacrylate polymer and an methacrylate polymerother than methyl methacrylate polymer.

Inorganic and organic fillers may be added into the compositions of oneor two components denture base. Useful inorganic fillers include glass,metal ceramics, silicon dioxide in powdery or fiber format, which arepreferably silanized with coupling agent, such as3-methacryloxloxypropyltrimethoxy. Organic fillers include splinter orbead polymers of high molecular weight , or fibers such as aramidefibers, polyacrylate fibers, polyamide fibers and polyacrylonitrilefibers. Organic fillers may be used alone or mixed with inorganicfillers.

Thermoplastic compounds such as poly functional methacrylate,polycarbonate, polysulfone, fluoropolymers, elastomers, polyurethanes,impression compound, wax, gutta percha, polycaprolactone and mixture ofthermoset and thermoplastics are advantageously heat processed with theprovided method and permit dental rehabilitation.

Microwave absorbing substances can advantageously be incorporated intodisclosed thermoplastic and thermohardening material compositions, todecrease internal heat generation of compositions which does not havesufficient dielectrical loss when microwaved nor does they havesufficient heatability for a desired speed of heating. These microwaveabsorbants are also useful when the employed polymeric material has onlya low microwave absorption behavior at low temperatures such as manythermoplastic polymers including polycarbonate and also forsubstantially increasing the speed and the addressability such as inwelding and joining functions. These absorbers may be powdery, hollowed,coated and comprise ferromagnetics, metallic oxides or specialityceramics. Microwave absorbant materials and or sterilants can beadvantageously utilized with the intra-oral embodiment of the presentinvention to increase the speed and addressability of heating the dentalcomposite and to increase the effectiveness of the sterilization of thetargeted caries.

The following tables set forth several examples in accordance with thevarious aspects of the present invention. All ratio for materials areexpressed in weight.

Experiment of decay control in the cavity microwave applicator

Preparation Microwave irradiation Incubation Results Section of decayousfreshly Surface desinection, 1.5 W/cm² energy Culture of irradiated-Microwave extracted human teeth 15 seconds deeping density ofirradiation & non irradiated irradiation destroy prepared, 2 mm³ incloramine T (200 W in the cavity witness decayous 80% carious zonesolution applicatior) teeth sections in a microorganisms 60 sec. mediumat -Witness teeth 37° C. 24 h. cultures cloudy

What is claimed is:
 1. A microwave dental system comprising: a hand-helddental tool including: an antenna positioned at a distal end of the tooland configured to be selectively positioned within a mouth of a patientadjacent at least one tooth; and a waveguide connected to the antenna; asource of microwave energy operably coupled to the waveguide, includinga control system for controlling delivery of microwave energy to thewaveguide, the control system including a feedback sensor such that themicrowave energy is applied to the tooth to allow the feedback sensor todetect the existence of caries in the tooth.
 2. The microwave dentalsystem of claim 1 wherein control system controls the source ofmicrowave energy to deliver less than 10 W to the antenna.
 3. The systemof claim 1 wherein the control system operates the source of microwaveenergy at voltages in a range of between 10 and 65 V.
 4. The system ofclaim 1 wherein the control system operates the source of microwaveenergy at frequences of between 1 GHz to 50 GHz.
 5. The system of claim1 wherein the control system operates the source of microwave energy atfrequencies between 14 GHz to 24 GHz.
 6. A method for intra-orallytreating caries comprising: identifying a carious lesion in a tooth in apatient's mouth; and using a hand-held dental tool to intra-orally applymicrowave energy to at least one exterior surface of the tooth tonon-invasively treat the carious lesion.
 7. The method of claim 6wherein the hand-held tool includes a sensor for measuring microwaveenergy absorbed by a tooth and wherein the carious lesion is identifiedby determining an amount of microwave energy absorbed by the toothindicative of a carious lesion.
 8. The method of claim 6 furthercomprising: applying a sealant to the tooth after the application ofmicrowave energy.
 9. The method of claim 6 wherein a portion of thecarious lesion is mechanically removed prior or after to the applicationof microwave energy.
 10. The method of claim 6 further comprising:applying a resin matrix to the tooth; and using the hand-held dentaltool to polymerize the resin matrix.
 11. The method of claim 6 whereinhand-held tool includes an antenna that is operatively coupled to asource of microwave energy by a waveguide and wherein the source ofmicrowave energy is operated to deliver less than 10 W of microwaveenergy to the antenna.
 12. The method of claim 11 wherein the source ofmicrowave energy is operated at voltages in a range of between 10 and 65V.
 13. The method of claim 11 wherein the the source of microwave energyis operated at frequences of between 1 GHz to 50 GHz.
 14. The method ofclaim 13 wherein the source of microwave energy is operated atfrequencies between 14 GHz to 24 GHz.